====== Improve vt(4) splash screen support ======

| Repository | https://github.com/0mp/freebsd/tree/splash-vt |
| Bugzilla | https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=210432 |

===== Overview =====

At the moment (2018-09-11) vt(4) has very limited support for splash screens.

The goal of this project is to extend it a little bit. It should be possible to:

  * load a specified BMP file to be displayed as splash screen
  * control display colors via kernel tunables

A stretched goal is to support bitmaps with the color depth of more than 1.

===== Roadmap =====

| Add sysctl tunables for splash colors in vt(4). | {o} |

===== References =====

  * [[https://www.freebsd.org/cgi/man.cgi?query=splash&manpath=FreeBSD+11.2-RELEASE+and+Ports|splash(4)]]
  * [[/Newcons]]
  * [[https://en.wikipedia.org/wiki/BMP_file_format|BMP file format (Wikipedia)]]

==== Mailing list threads ====

  * [[https://lists.freebsd.org/pipermail/freebsd-hackers/2018-September/053329.html|Let's improve splash screen support in vt(4) (freebsd-hackers@, 2018-09-11)]]

===== Research =====

Commit adding some splash screen support to vt(4): 2ecca071d5eccf38f9a5fd7a03052b261b7bd7d2

sc(4) supports 8-bit colors.

Interesting functions:

  * ''%%vd_bitblt_bmp%%''
  * ''%%vt_fb_bitblt_bitmap%%'' (vt_fb.c)
  * ''%%vt_fb_setpixel%%'': it seems to be the function which is capable of setting pixel colors in a console controlled by vt(4).

==== The vtterm_splash function ====

There's a function called ''%%vtterm_splash%%'' in ''%%vt_core.c%%'', which displays a boot splash when the kernel is compiled with ''%%DEV_SPLASH%%'' option, textmode is not activated and a muted booting was requested by the user (for example via specifying ''%%-m%%'' to boot(8%%))%%.

Also the following part of the ''%%vtterm_splash%%'' function:

<code c>
switch (vt_logo_depth) {
case 1:
        /* XXX: Unhardcode colors! */
        vd->vd_driver->vd_bitblt_bmp(vd, vd->vd_curwindow,
            vt_logo_image, NULL, vt_logo_width, vt_logo_height,
            left, top, TC_WHITE, TC_BLACK);
</code>

<sup>Source: vt_core.c</sup>

suggests that:

  - Monochrome colors are the only one supported at the moment.
  - It should not be complicated to add support for 4-bit and 8-bit colors.
    * Actually, there is an sc(4) file, which has a very similar switch construct handling various color depth configurations.
      * What's the name of the sc(4) function with that switch case?
        * There's no such function in sc(4). There is ''%%bmp_SetPix%%'' in ''%%sys/dev/fb/splash_bmp.c%%'' but it does not help much as it directly sets video bits. Its signature looks like this:  ''%%static void bmp_SetPix(BMP_INFO *info, int x, int y, u_char val)%%''.

Other questions regarding the ''%%vtterm_splash%%'' function:

  - {o} What is the ''%%VDF_SPLASH%%'' flag inside ''%%vd->vd_flags%%'' for?
  - {o} How to load a BMP file into a structure accepted by functions displaying pixels? Could it be that the splash(4) driver provides all the required functions to do so? Ideal scenario:
    - The splash(4) driver reads the bitmap file that was specified in loader.conf(5) and converts it to a structure accepted by internal vt(4) functions.
    - vt(4) gets the structure from splash(4).
    - vt(4) displays the bitmap.
  - {o} How does the ''%%vd->vd_driver->vd_bitblt_bmp%%'' function work?
    * ''%%struct vt_driver%%'' seems to be an interface for different hardware have to implement in order to use the vt(4) driver. ''%%vd_bitblt_bmp%%'' happens to be one of the drawing functions. It has various implementations like ''%%ofwfb_bitblt_bitmap%%'', ''%%vga_bitblt_bitmap%%'' or ''%%vt_fb_bitblt_bitmap%%''.

At the moment the vt(4) driver stores logos in ''%%unsigned char%%'' structures (see ''%%sys/dev/vt/logo/logo_beastie.c%%''), which roughly correspond to the ''%%u_char *data%%'' member of the ''%%BMP_INFO%%'' structure (see ''%%sys/dev/fb/splash_bmp.c%%'').

<code c>
typedef struct
{
    int     width,height;           /* image dimensions */
    int     swidth,sheight;         /* screen dimensions for the current mode */
    u_char  depth;                  /* image depth (1, 4, 8, 24 bits) */
    u_char  sdepth;                 /* screen depth (1, 4, 8 bpp) */
    int     ncols;                  /* number of colours */
    u_char  palette[256][3];        /* raw palette data */
    u_char  format;                 /* one of the BI_* constants above */
    u_char  *data;                  /* pointer to the raw data */
    u_char  *index;                 /* running pointer to the data while drawing */
    u_char  *vidmem;                /* video memory allocated for drawing */
    video_adapter_t *adp;
    int             bank;
} BMP_INFO;
</code>

<sup>Source: sys/dev/fb/splash_bmp.c</sup>

<code c>
const unsigned char vt_beastie_vga16[] = {
        0x16, 0x00, 0x62, 0x16, 0x88, 0x03, 0x80, 0x16, 0x00, 0x23, 0x88, 0x80,
        0x00, 0x00, 0x08, 0x88, 0x16, 0x00, 0x21, 0x08, 0x16, 0x00, 0x06, 0x88,
        0x16, 0x00, 0x20, 0x80, 0x16, 0x00, 0x06, 0x08, 0x80, 0x16, 0x00, 0x1e,
</code>

<sup>Source: sys/dev/vt/logo/logo_beastie.c</sup>

==== Glossary ====

  * **DIB**: device independent bitmap

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{{tag>Project}}